Rapid Autoregulation of Cerebral Blood Flow: A Laser-Doppler Flowmetry Study

Abstract

The mechanisms underlying autoregulation of CBF were studied in 19 rabbits using laser-Doppler flowmetry. A cranial plexiglas window was chronically inserted in the skull with dental cement under general anesthesia. The animals then were reanesthetized 5-7 days later and subjected to aortic bleeding while CBF was measured with the probe placed on the window. In the first set of experiments, MABP was decreased (from 90 to 30 mm Hg) and was maintained constant for 1 min. During the first seconds, CBF followed the steep decrease of MABP. Then, CBF increased and reached a plateau within 3-13 s, depending on the severity of hypotension. Hyperemia occurred when blood was restored, and the CBF recovered from this posthypotensive hyperemia with a rapid phase (within 2 s) and a slow phase (total recovery within 1 min). The lower limit of autoregulation was found to be 40 mm Hg. An increase in CBF due to papaverine showed that vasodilation was not maximal below this limit. In the second set of experiments, the rabbits were subjected to four episodes of hypotension at 40 mm Hg each but of different durations (from 2-3 to 60 s). The posthypotensive hyperemia was not influenced by the duration of hypotension, but the time of the total recovery phase increased with the duration of hypotension. We conclude that there exist rapid adaptive mechanisms leading to autoregulation and that the vasodilation is not dependent upon the duration of hypotension.

Is the Acetazolamide Test Valid for Quantitative Assessment of Maximal Cerebral Autoregulatory Vasodilation?

“…In animals, assessments of the autoregulatory capacity are ideally based on (1) imposed acute blood pressure variations and (2) online simultaneous CBF measurements. 9 Classically, decreases in MABP are obtained by …”

“…Arterial bleeding induces hypovolemia, hypocapnia, and alkalosis, 9 but it produces rapid and controlled hypotension. Anesthesia obtained by ␣-chloralose plus halothane allows studies of the cerebrovascular reactivity inasmuch as its effects on this reactivity are only transient.…”

“…9 In experimental studies, one advantage of the ACZ test 1,5 is that it only necessitates an intravenous injection. In humans, the ACZ test is safe, inasmuch as it does not induce large blood pressure variations.…”

“…CBF was measured during the last 30 seconds to allow autoregulatory mechanisms to be effective at each MABP level. 9 MABP was reduced to 20 mm Hg, which is below the lower limit of CBF autoregulation (40 to 60 mm Hg), to ensure that the maximum of autoregulatory vasodilatation was reached. Blood was then reinfused, and the rats were killed by barbiturate injection.…”

Digital Imaging of Umbelliferone Clearance: A Method for Repeated Measurements of Cerebral Cortical Blood Flow with High Temporal and Spatial Resolution

“…et a!., 1964; Obrist and Wilkinson, 1990), and laser Doppler flowmetry (Florence and Seylaz, 1992)]. The most widely reported and relatively simple method of hydrogen clearance is invasive, and the varying effects of electrode cortical puncture, elec trode size, and the chronicity of electrode implan tation on regional cerebral blood flow (reB F) esti mations are well documented (Scremin et a!., 1973;Rosenblum, 1977;Lauritzen, 1984;Benveniste et a!., 1987;Jackowski et aI., 1989;Tomida et aI., 1989;Piper et a!., 199 1;Verhaegen et aI., 1992).…”